Our research objectives are to understand biological processes and phenomena in terms of physical mechanisms and to explore the adaptation of physical techniques to problems in biology. The more specific goals and problems to which we are addressing ourselves are the following: 1.) The mechanism of energy conversion in a protein-chlorophyll complex solubilized frm the membranes of photosynthetic bacteria and the characterization and determination of the structure function relation of this complex called the reaction center (RC). Specific aims are to: (a) complete the amino acid sequence of the RC protein, (b) to obtain the three-dimensional structure of the RC by X-ray diffraction, (c) to investigate the effect of protein modifications on the structure and funciton of the RC, and (d) to extend the investigation to other membrane proteins. Some of the findings and methodologies are expected to be relevant to other electron-transfer processes, most notably the respiratory chain in mitochondria. 2.) Electronic Structure of Biomolecules: We want to extend our understanding of the non-heme iron center of RCs to the atomic (molecular) level. EPR and ENDOR experiments will be used to determine the parameters characterizing the electronic state of the Fe2+. 3.) Crystallization of Biological Macromolecules, with special emphasis on proteins. Our goal is to understand the detailed mechanisms leading to the formation of single crystals. The three temporal phases of crystallization, i.e., a.) nucleation, b.) post-nucleation growth, and c.) cessation of growth, will be investigated on the water-soluble model compound. lysozyme. We plan to extend the methodology to other proteins, including integral membrane proteins. The long-term objective is to arrive at a systematic procedure to obtain large, high-quality crystals for X-ray diffraction studies.